Device in a reactor for gasifying spent liquor

ABSTRACT

This invention relates to a device for thermal decomposition of stock, especially a spent liquor obtained from pulp manufacture, where the gas stream formed in this connection passes through a liquid bath. The decomposition device has a reactor with a chamber in which thermal decomposition takes place, and a separation zone including a liquid bath for separating off components contained in the gas stream leaving the chamber. The separation zone includes a housing for the liquid bath and a tipping chute arranged adjacent the outlet of the chamber, so that the tipping chute at least partially increases in cross-sectional area in the direction of flow of the gas stream.

TECHNICAL BACKGROUND

The present invention relates to a device for thermal decomposition ofstock, especially a spent liquor obtained from pulp manufacture, wherethe gas stream formed in this connection contacts a liquid bath, inwhich smelt particles are separated from the gas. The device comprises areactor and a housing for the said liquid bath inside which a tippingchute, which is connected to the outlet of the reactor chamber,discharges.

STATE OF THE ART AND PROBLEMS

In the production of pulp, spent liquors are generated which containboth inorganic and organic compounds. It is desirable to recover theinorganic compounds, in order to produce new digestion liquid, and toextract fuel energy from the organic compounds. A special method forachieving this is described in WO-A-SE91/00383. Instead of theconventional recovery boiler, a gasification reactor is used in whichthermal decomposition of the spent liquor takes place under conditionsof sub-stoichiometric oxygen supply, so that a large amount ofcombustible gases (CO, H₂, CH₄, H₂ S, etc.) is produced in the reactor.The fuel energy in these gases can then be employed in a flexiblemanner, for example for steam generation or for gas turbine operation.

However, during the thermal decomposition, a mixture is formed of thesaid gases and finely-suspended inorganic components. The inorganiccomponents must be separated from the gas stream before the gas can beused as a multi-purpose fuel. According to the above mentioned knownmethod, the main separation takes place in a liquid bath which isarranged in direct connection to the reactor outlet. Using a tippingchute, whose lower end discharges into the liquid bath and whose upperend is arranged at the outlet of the reactor chamber, the gases areconducted down into the liquid bath, in which liquid bath the said mainseparation occurs.

By means of a follow-up treatment of the liquid in the liquid bath, theinorganic components can be recovered for renewed use. The gas is alsosubjected to a follow-up treatment before it is utilised as fuel.Included in the latter follow-up treatment are heat exchange of thecombustible gases to extract the physical heat (thermal energy) theypossess, and also scrubber treatment.

Liquid is added both to avoid problems resulting from depositions ofsolidified smelt at the outlet of the reactor chamber, and also toprotect the inner surface of the tipping chute both from chemical attackand from high temperature. An additional arrangement in association withthe outlet of the reactor chamber consists of cooling loops which arearranged on the outer surface of the bottom cone.

It is evident to the person skilled in the art that both thesearrangements are relatively comprehensive and expensive, as a result ofthe separate pumping, piping and controlling systems which arenecessary, for which reason it is desirable to avoid these completely. Afurther problem is that small alkali particles (in the form of fumes)are not separated off in a known kind of quench.

SOLUTION AND ADVANTAGES

An object of the following invention is to present a reactor in whichthe above mentioned disadvantages are eliminated. The invention alsoprovides the advantage that a greater flow of liquid on the inner wallof the tipping chute can be obtained, which implies that strongerinstantaneous cooling, so-called quench cooling, of gas and smelt dropscan be obtained, as can improved dissolution of the smelt particlesalready in transit down through the tipping chute. Secondly it is anobject to present a reactor which does not possess special arrangementscomprising piping, pumps and control equipment for supplying liquidinside the tipping chute or for cooling the bottom cone of the reactorchamber.

The above mentioned object is achieved using a device for thermaldecomposition of stock, especially a spent liquor obtained from pulpmanufacture, where the gas stream formed in this connection contacts aliquid bath, which device comprises a reactor with a chamber for thesaid thermal decomposition and a separation zone including a liquid bathfor separating off components contained in the gas stream leaving thechamber, where the said separation zone comprises a housing for the saidliquid bath and a tipping chute arranged in association with the outletof the chamber, characterised in that said tipping chute at least partlyhas an increasing cross-sectional area in the direction of flow of saidgas stream.

By means of the invention a desired cooling of the bottom cone may beachieved in combination with a desired flow of liquid through thetipping chute. Moreover the invention provides for that it eliminatesthe need for expensive equipment.

Other advantages of the invention are that the improved circulationprovides speedier and more effective cooling of the gas and thatformation of encrustations is counteracted. Additionally, the genesis of"fumes" (very small particles 0.1-1 μm) is counteracted and/or veryprobably eliminated, since the gas with its content of chemicals iscooled and wetted by the liquid supply immediately after the reactoroutlet, which leads to instantaneous condensation or absorption of thesodium content.

BRIEF DESCRIPTION OF THE FIGURES

The invention will be explained in more detail below with reference tothe attached figures, in which:

FIG. 1 shows a reactor according to known technology in cross-section

FIG. 2 shows diagrammatically the lower part of a reactor comprising adevice according to the invention,

FIG. 3 shows the lower part of a reactor arranged with a firstembodiment of a device according to the invention,

FIG. 4 shows a preferred embodiment of a device according to theinvention,

FIG. 5 shows an alternative embodiment of a device according to theinvention,

FIG. 6 shows a modified design of a device for gasification of blackliquor,

FIG. 7 shows a further alternative embodiment,

FIG. 8 shows a gas/liquid scrubber intended to be coupled to a reactordevice according to the invention, and

FIG. 9 shows a further gas/liquid scrubber device.

FIG. 1 shows a cross-section in the vertical direction of a knownreactor 1 for gasifying black liquor. The reactor comprises an upperpart 1A with a chamber 3 inside which thermal decomposition takes placeof the black liquor introduced through the inlet part 2. During thisthermal decomposition, a gas G is produced containing finely dividedinorganic smelt particles. This gas then passes out through the loweroutlet orifice 5 of the chamber 3. The lower part 1B of the reactor 1constitutes a part for cooling, partial dissolution and separation forthe hot gas with inorganic particle content flowing out from the outletorifice 5.

The lower part 1B comprises a housing 8B inside which a liquid bath 7 ismaintained. The gas G is conveyed down into the liquid bath 7 by meansof a tipping chute 6 which is arranged with its upper end at the outletorifice 5 of the chamber 3. The gas is led down into the liquid bath bythe opening 6B of the tipping chute discharging underneath the surface7A of the liquid bath. In the liquid bath 7, the gas is forced to movealong a given path using an ascending pipe 15 which is arranged outsidethe tipping chute 6. In the liquid bath 7, the gas is cooled and theinorganic components are dissolved in the liquid and separated from thegas. The gas purified in this manner is then led out of the reactor 1via a pipe conduit (not shown). The inlet to the latter pipe conduit isarranged in the lower part 1B of the reactor, somewhere above thesurface 7A of the liquid bath.

FIG. 2 shows an outline diagram of a device according to the invention.The outer broken line indicates the bottom part 1B of the reactor,inside which is found the liquid bath 7. In addition, the figure showsthe lower part of the reactor chamber 3, which has a ceramic lining, itsbottom part 4 and in particular its outlet section 5. This section 5consists of a conical upper part 11 at which is arranged a cylindricalorifice part 12. Coaxially in relation to the said outlet section 5,there is arranged a tipping chute 6. The upper section of the tippingchute is cylindrical and arranged to overlap in relation to thecylindrical part 12 of the outlet section 5. Between the tipping chute 6and the cylindrical orifice part 12 a ring-shaped gap 9 is formed. As aresult of being able to move the tipping chute 6 in the verticaldirection, the size of the gap can be regulated. When this is done, theupper end of the tipping chute 6 comes, in an upper extreme position,into contact with the outside of the conical section 11 of the outletsection 5 of the chamber, so that there is no gap between these twoparts. By moving the tipping chute downwards from this extreme position,the size of the gap can consequently be gradually increased.

As a result of the ejector effect from the gases passing out through theoutlet section 5, the liquid in and around the gap is caused tocirculate, in accordance with the Venturi effect, which can be derivedfrom Bernoulli's equation. By additionally arranging an ascending pipe15 outside the tipping chute 6, a so-called "mammoth pump effect" isadditionally obtained, which effect creates a very favourablecirculation in the liquid bath, so that the gases which are passing outare cooled quickly and the inorganic particles simultaneously separatedout. By regulating the ring gap, the flow of liquid in the liquid bathmay consequently be regulated so that a desired portion flows into thetipping chute 6 and another desired portion flows up along the outsideof the bottom cone 4 of the reactor chamber 3, as has been indicated bythe flow arrows in the diagram.

FIG. 3 shows a preferred embodiment of the bottom part 1B of a reactoraccording to the invention. Accordingly, the figure shows the lower partof the reactor chamber 3 and its orifice section 5 which is arrangedconcentrically in relation to the conical bottom section and hascylindrical orifice part 12. Encircling the end of the orifice there isarranged a U-shaped ring element 5A which is U-shaped in cross-sectionand which is positioned so that the shanks essentially extend along thecentre line 10 of the reactor 1. As a result of the curve in the bottomsection of this U-shaped ring element 5A, a delimitation surface 64 isformed which determines the size of the gap 9 in relation to the upperedge of the tipping chute 6. The outer shank 13 of the U-shaped ringelement 5A forms a collar-like part which divides the liquid flow risingupwards between the tipping chute 6 and the ascending pipe 15 into astream which passes into the tipping chute 6 and a stream which passesupwards towards the outside of the bottom section 4 of the gasificationchamber 3. The amount of the flow going in one direction or the other isdetermined primarily by the size of the gap, the speed of the exitinggas and the prevailing pressure conditions. The size of the gap isdetermined, as has already been described, by the tipping chute 6 beingmovably arranged (not shown) along the centre line 10.

In this example, a very favourable flow is obtained for cooling thebottom cone 4 owing to a collar element 16 which has been arranged ontop of the ascending pipe 15. This collar element 16 extends for asubstantial distance along the bottom cone and with about the sameconicity as the bottom section 4. In this way the liquid is obliged toflow up along the bottom cone 4. For gas removal there is arranged apipe conduit 17 whose inlet opens in a pocket 18 between the collar 16,arranged on the ascending pipe 15, and a downwardly-directed flange 16Aat the upper end of this collar. Addition of new liquid suitably takesplace through an inlet 26 which is arranged to open out in the vicinityof the lower ring gap between the ascending pipe 15 and the tippingchute 6. Removal of liquid from the liquid bath 7 is suitably achievedvia an output 27 which is arranged in the lower part of the bottomsection.

As is indicated by the arrows, the gases leaving the chamber 3 will passout of the orifice section 5 and, in doing so, affect the ring gap 9,between the tipping chute 6 and the ring-shaped element 5A, so that alower pressure arises in the region around the gap (Venturi effect)which causes liquid from the liquid bath to flow into the tipping chute6. The amount and distribution is regulated by regulating the gap size,which in turn is regulated by raising or lowering the tipping chute 6.The gases with inorganic content leaving the chamber 3 will thus alreadybegin to be mixed with liquid in the tipping chute 6 and rapid coolingand separation of the gas is begun while at the same time depositions onthe inside of the tipping chute 6 are avoided. As has already beenindicated, this addition of liquid, in the optimum case, counteracts thegenesis of "fumes". Once the gas has reached the lower end of thetipping chute 6, it will turn up and ascend upwards along the ring gapwhich is formed between the tipping chute 6 and the ascending pipe 15.In doing this, the gas will also suck with it some liquid from the spaceoutside the ascending pipe 15 ("mammoth pump effect"), i.e. liquid issucked in from outside and into the ascending pipe 15 by the liquidbeing drawn down and in underneath the lower edge of the ascending pipe,which edge is located at a lower level than the corresponding edge ofthe tipping chute 6. With the aid of the ascending gas, and the liquidmixed in with it, cooling is achieved of the bottom cone 4. Finally thepurified gas arrives in the gas pocket 18 and flows out via the pipeconduit for gas removal 17.

FIG. 4 shows a preferred embodiment of the invention which is somewhatmodified in relation to that which is shown in FIG. 3, whereby, insteadof a collar extension on the ascending pipe 15, a separate collar baffle60 is arranged on the bottom section 4 of the reactor. Using thisdesign, the pipe conduit for gas removal 17 can be arranged directly inthe mantle 8 at a level above the aforesaid collar 60. Additionally,FIG. 4 shows how a tipping chute 6, in a preferred manner, may bearranged so that it can be raised and lowered. An axle 22 with anoperating member 24 is fixed along the centre line 10 with the aid of astuffing box 23 in the bottom. The axle 22 is engaged with a nut 20which is fixed inside the tipping chute 6 with the aid of stays 21 inthe vicinity of the lower end of the tipping chute 6. Guide bars 25 arearranged on the inside of the upper end of the tipping chute, whichguide bars first and foremost have a centering function but also preventthe tipping chute from being rotated around the centre line 10. Byturning the operating member 24, it is thus possible to move the tippingchute 6 upwards or downwards.

FIG. 5 shows, according to an alternative embodiment, that the collar 60can be arranged directly on the U-shaped ring orifice element 5A,whereby a predetermined division is obtained of the circulation flowinto an outer and an inner flow for rapid cooling in the tipping chute6.

Additionally it is shown that the tipping chute 6 is divided into afixed part 26 (fixed either to the ascending pipe 15 or to the mantle 8)and a movable, upper part 6A. Using this arrangement, the lower edge ofthe tipping chute 6 can always be kept at an optimal distance withrespect to the lower edge of the ascending pipe, independently of theoptimal gap width at the reactor orifice 5. In addition, centering ofthe movable upper part 6A is obtained in a relatively simple manner.

FIG. 6 shows a modified embodiment of a tipping chute according to theinvention where the tipping chute 6 is fixed in relation to remainingparts and is designed to be supplied with external liquid, with quenchcooling, by means of a nozzle ring 27 which is fed with liquid via aconduit 28 coming from the outside. However, in this example too, thecooling of the bottom cone 4 is achieved in accordance with that whichhas previously been described.

As has previously been pointed out, one of the objects of the inventionis to improve the dissolution ability of the inorganic particles in thecombustible gas in a controllable manner. FIG. 7 shows an embodimentwhich has the object of improving this ability still further, in whichnozzle ring 27 and conduit 28 are provided as in FIG. 6. In the vicinityof its middle section, the ascending pipe 15 is shaped so that theflow-through area along a limited section 15A is substantially narrowerthan at other sections of the space between ascending pipe 15 andtipping chute 6. This shape elicits turbulence which leads to fasterdissolution and cooling of the inorganic particles in the liquid.Additionally, the figure shows that, in the preferred embodiment,provision can be made for adding further liquid, by means of an intakeconduit 29 and the multiplicity of inlet pipes 30, at the narrowerlimited 15A. In order to increase dissolution ability still further, itis proposed, in accordance with this embodiment, that static mixerelements 31 be arranged between ascending pipe 15 and tipping chute 6.These mixer elements may advantageously be shaped in accordance with thedescription given in Chemical Engineering, July 1989, page 137, ff."Better Absorption? Try a static mixer", i.e. a static mixer accordingto one of the four general alternatives dual-blade, corrugated-plate,intersecting-bar or helical, which therefore consist of plates arrangedin a special manner and/or bars which, because of their mutualorientation, force the gas and/or liquid to move in a particular manner.

It will be evident to the person skilled in the art that the quenchdevices shown previously may also be equipped with such static mixers,if this is required.

FIG. 8 shows a gas/liquid scrubber 32 designed to be used in some stageafter a previously described reactor with a view to purifying the gas tothe extremely low levels which are necessary in connection with gasturbine operation. Like the quench solution shown in FIG. 7, thisscrubber is constructed with the aid of static mixer elements 31. Thescrubber consists of an inlet arrangement 33 for combustible gas and aninlet arrangement 62 for the addition of liquid. Both these inletarrangements 33, 62 discharge in the upper end of a long pipe 34, 35.The previously mentioned static mixer elements 31 are arranged insidethis pipe. The lower part of the scrubber comprises an outer housing 36inside which the pipe 34, 35 discharges 37, and inside which a liquidbath 39 is arranged together with outlet members for gas and liquid, 40and 42 respectively. The outlet member 40 for the gas is attached to apipe part 38 which possesses openings above the liquid level 41 in theoutlet housing 36. The static mixer elements 31 are arranged in theupper part in such a way that the direction of flow is reversed onseveral occasions while in the lower part of long pipe 35, mixingelements 31 are arranged which continuously conduct the gas flow in thesame direction of rotation, thereby causing the liquid and other heavierparticles to be centrifuged out towards the periphery. The scrubber thusfunctions in such a way that the hot gases enter the inlet 33 and intothe upper part of the long pipe 34 where the gases are brought intocontact with a liquid, preferably an alkaline liquid for absorption ofH₂ S, during a short but intensive exposure. The gas contains, interalia, H₂ S, CO₂, "fumes" and liquid drops. Mixing and scrubbing thustakes place in the upper part of the long pipe 34, during which theinorganic part of the gas is dissolved in the liquid which has beensupplied. In the lower part of the long pipe 35, liquid and otherheavier particles will then be separated from the gas due to centrifugalforce. This liquid and heavier particles then fall down into the liquidbath 39 while the purified and dry gas flows in through the suitablydisposed orifices which are present above the liquid level 41.Thereafter the gas is drawn off through the outlet member 40 arranged atthe bottom and the liquid is separately drawn off through the outletmember 42.

FIG. 9 shows a further embodiment in which static separator/mixerelements 31A, 31M are used. Here, a first separation of the gas leavingthe lower part of the reactor 3 takes place in the first separationsection 43 with separator elements 31A. A powerful addition of liquidtakes place through liquid supply 44 in conjunction with the reactoroutlet, which liquid cools the gas and condenses out inorganiccomponents which, together with the liquid, are forced to rotate bymeans of the separator elements 31A so that they are separated from thegas stream due to the centrifugal force. The liquid 47 is collected in avessel 45 from which it can be led away via a conduit 49, so that thequantity of liquid can be kept constant. The gas continues into a pipe48, containing a scrubber with liquid addition through liquid supply 46;and mixer elements 31M, in which gas and liquid are brought intointimate contact by continuous changes in direction which are caused bythe mixer elements 31M. After that, a second separation takes place in asubsequent vessel 50, once again by means of separator elements 31A. Thepurified gas is then received in pipe 51 taken out via a pipe 54 whilethe liquid which has been separated off is collected in a container 52with an outlet conduit 53. Liquid from this container 52, like that fromthe first vessel 45, may advantageously be used as an addition to one ofthe supplies 44, 46. By means of this approach, different concentrationsof chemicals can be obtained in a selective manner in the drawn-offliquids, thereby facilitating optimal chemical recovery.

It will be evident to the person skilled in the art that the inventionis not limited by that which has been described above, but can be variedwithin the scope of the subsequent patent claims. Thus it is obviousthat the gap can be formed in another manner, for example by having thetipping chute 6 flexibly arranged at one edge of the reactor orifice. Afurther method would be to have a movable casing arranged on the outsideof the upper part of the tipping chute, and consequently, by moving thesaid casing up or down, the gap 9 between tipping chute and orificesection 5 can be regulated. Other conceivable embodiments areoverlapping perforated rings, which, at different relative positions,expose continuous openings of varying size which permit communicationbetween the liquid bath and the inside of the tipping chute.Furthermore, it is obvious that other methods can be used for moving thetipping chute than that which has been shown, for example hydraulics,pneumatics, pinion and rack etc.

I claim:
 1. A device for thermally decomposing stock, comprising:areactor having a chamber in which thermal decomposition takes place,said chamber having an outlet; and a separation zone comprising ahousing containing a liquid bath for separating out components containedin a gas stream leaving the chamber, and a tipping chute; wherein saidtipping chute has a first and a second end, said first end beingdisposed adjacent said outlet of the chamber, said second end beingdisposed within the housing for containing the liquid bath; and whereina cross-sectional area of said second end of said tipping chute islarger than a cross-sectional area of said first end of said tippingchute.
 2. The device of claim 1, further comprising:means for injectingcooling liquid into the gas stream at approximately a most narrowportion of said tipping chute and said outlet.
 3. The device of claim 2,wherein said means for injecting cooling liquid is constructed andarranged to add said liquid in the form of one of a downwardly flowingfilm along the inner surface of the tipping chute and a spray.
 4. Thedevice of claim 2, wherein the most narrow portion of said tipping chuteand said outlet is formed by an outlet of said reactor.
 5. The device ofclaim 1, wherein the second end of the tipping chute is located at aposition which is below a surface level of the liquid bath.
 6. Thedevice of claim 1, wherein at least one opening is formed in a wall ofthe tipping chute, which during operation permits communication betweenan inside of the tipping chute and liquid from the liquid bath.
 7. Thedevice of claim 1, further comprising an ascending pipe disposed withinthe housing and outside the tipping chute.
 8. The device of claim 1,wherein a portion of the tipping chute increases conically incross-section.
 9. The device according to claim 8, wherein the means forinjecting cooling liquid is positioned above the portion of the tippingchute which increases in cross-sectional area.